There are a large number of functions and operators
available in POSTGRESQL. Function calls take zero, one, or more arguments
and return a single value. You can list all functions and their arguments using
psql's \df command. You can use psql's \dd
command to display comments about any specific function or group of functions,
as shown in figure .
Operators differ from functions because they are accessed using symbols, they
always take two arguments, and the two arguments appear to the left and right
of the operator symbol. For examples, + is an operator that takes one
argument on the left and one on the right, and returns their sum. Psql's \do
command lists all POSTGRESQL operators and their arguments. Figure
shows operator listings and operator use.